encompass-cs-docs/content/concepts/component.md

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---
title: "Component"
date: 2019-05-22T12:51:29-07:00
weight: 5
---
A Component is a collection of related data.
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To define a Component, declare a struct which implements the **IComponent** interface.
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```cs
using Encompass;
using System.Numerics;
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public struct VelocityComponent : IComponent {
public Vector2 velocity;
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}
```
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Components are attached to Entities with the **SetComponent** method.
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```cs
using Encompass;
...
var worldBuilder = new WorldBuilder();
var entity = worldBuilder.CreateEntity();
worldBuilder.SetComponent(entity, new VelocityComponent { velocity = Vector2.Zero });
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```
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**SetComponent** can also be used from within an **Engine**. We will talk more about this later.
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Components are always structs, meaning they follow value-type semantics. If you are used to working with classes you might find this confusing.
One major point of difference is that value types are _copied_ rather that passed by reference by default.
You can read more about value types here: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/value-types
If you use them idiomatically, you don't have to worry about them creating garbage collection pressure, so this is a big win for performance when working in C#.
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{{% notice warning %}}
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Components should **never** reference other Components directly. This breaks the principle of loose coupling. You **will** regret it if you do this.
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{{% /notice %}}